The last images returned to Earth had been taken in March 2013. The photo below includes data from 96 of those images. It may not look very impressive, but the comet was still nearly 4 AU away at the time that these photos were taken. The long streaks in the background are stars; the small dots are from hot pixels on the camera detector.
NASA / JPL / UMD / Emily Lakdawalla
Deep Impact's final observations: Comet ISON
This image of comet ISON is a stack of 96 photos taken with Deep Impact's Medium Resolution Imager on March 9 and 10, 2013. The image is enlarged from the original resolution by a factor of 4. The comet was about 3.9 AU from Deep Impact at the time. These are the last images that Deep Impact returned to Earth before failing in August 2013.